U.S. Pat. No. 3,231,437 discloses a detonable water-in-oil emulsion comprising nitroglycerin and an ionic emulsifier and a stabilizer such as collodion-cotton. These nitroglycerin emulsions were reported to be safe in transport or storage using about 1% by weight ionic emulsifier such as sodium cetyl sulphate, magnesium oleate, calcium stearate and zinc stearate.
U.S. Pat. No. 4,767,476 discloses a process and device for temporary storage of oil-in-water nitroglycerin emulsions. A disadvantage of this system was a continuing need to provide agitation to avoid the settling out of drops of nitroglycerin from the emulsion.
U.S. Pat. No. 5,120,375 discloses an aqueous explosive composition in which ammonium nitrate is emulsified with a surfactant from the group of sorbitan monooleate, polyisobutylene succinic anhydride and hydrogenated tallow amine. In particular, it was disclosed that particles of ammonium nitrate with acid sites on the surface are substantially neutralized by basic groups on the surfactant during the production of stable emulsions. Determination of both type and the amount of surfactant to produce emulsification required actual experimental testing, since theory was unable to predict what was or was not satisfactory for emulsification. In addition, the emulsification of the explosive component these water-in-oil and melt-in-fuel emulsion explosives further comprised a cushioning agent such as cork or balsa to reduce predetonation sensitivity.
Hydrophile-Lipophile Balance (HLB) is a numerical method to characterize surfactants based on the size and length of the hydrophilic and lipophilic groups of the surfactant/emulsifier and was developed by ICI Americans Inc. (Wilmington, Del.). According to the theory involved, all surfactants with similar HLB values will have similar hydrophilic and lipophilic characteristics. Thus HLB value can be used to screen surfactants or emulsifiers once a desired effect has been observed.
The HLB system: A Time-Saving Guide to Emulsifier Selection. ICI Americas Inc., Wilmington, Del., 1976 provides a complete description of the Hydrophile-Lipophile Balance (HLB) system of surfactant selection including guidelines for tests to determine the required HLB value for a given system to be emulsified.
Yet despite what was known in the art, a need still existed for an oil-in-water explosive emulsion which remained stable for 24 hours or more without agitation.